Agricultural Microbiology

1. Introduction to Microbial World
Dr. S. PARTHASARATHY, M.Sc. (Agri)., Ph.D.
Assistant Professor (Plant Pathology)

2. This course deals with
 How and where the microorganism live
 Their structure, growth, nutrition, metabolism and energy
generation
 Metabolic diversity and classification
 Soil microbiology-nutrient transformations in soil, organic
matter decomposition
 Biological fertilizers

3. Scope of Microbiology & History
 Microbiology and microbial cell
 Groups of microorganisms
 Need for Microbiology
 Branches/ Scope of Microbiology
 Historical developments
Spontaneous generation Theory

4. Definition of Microbiology
• Microbiology: Study of microorganisms invisible to
naked eyes, that can exist as single cell or clusters.
Viruses are included, but are not cellular
• Microbial cell can live alone. Growth, energy
generation and reproduction are independent
• Plant & animal cells exist only as part of organisms &
depends on other cells for all processes.

5. Occurrence
• Occur every where
• Natural surfaces, hot springs, frozen sea ice
• Most are harmless to man, helps in many ways
• Microbes are the dominant forms of life in
earth, more than half the biomass on earth
consists of microorganisms

6. Branches of Microbiology
Medical Microbiology
Aquatic Microbiology
Aero Microbiology
Food Microbiology
Agricultural Microbiology
Industrial Microbiology
ExoMicrobiology
Geochemical Microbiology

7. History of Microbiology
• Obviously human have had to deal with microbes even
before the recorded history
• Babylonians were using yeast to make beer over 8000
years ago & acetic acid bacteria to make vinegar over
6000 years ago
• About 5000 years ago Persia region recorded wine
making

8. Robert Hooke (1635 -1700): One maker of microscope (30x
magnification) discovered the cell (Latin: cellulae meaning small
room). He noticed some microscopic fungi too.

9. • The first microscope by Antony van Leeuwenhoek (1632-1723)
• He discovered many small creatures he called “little
animalcules" in samples such as pond water.
• Father of Microbiology

10. Spontaneous generation theory
• Life arises from nonliving matter, spontaneously –A
biogenesis
• Ex. maggots were developed spontaneously via
recombination of matters in rotting materials (meat)
• Microbiology starts when the disprove of SG theory
• (a – not; bio – life; genesis – origin).

11. Arguments for SG Theory
• Francesco Redi (1626-1697)-support the SG
He established that the origin of maggot was from fly only
not from meat.
• John Needham (1713-1781)
Support the SG-Bacteria originated from meat
• Lazzaro Spallanzani (1729-1799)-
In boiled beef broth ,after sealing –he found no microbial
growth

12. Contd.
• (But till now, the supporters of SG theory believed that air is
essential for SG)
• Franz Schulze (1815-1873)
Passed air through strong acid before contact and so no
growth
• Theoder Schwann (1810-1882)
Passed air through hot tube before contact, so no growth
• H.Schroder and T.Von Dusch (1850)
Filter air through cotton plug

13. Louis Pasteur
Louis Pasteur (1822-1895) - (April 7,1864 )
 Conducted goose neck flask experiment. Passed the
untreated and unfiltered air in to boiled nutrient broth,
germs settled in the goose neck and no microbes appeared
in the solution
 His concept of Germ theory of disease (means germs are
responsible for the disease not the inert mater) ends the
SG theory.
 Ended the SG Theory

14. Louis Pasteur

15. John Tyndall (1820 -1893) :
• Proved that dust carries the germs and if no dust in the air,
sterile broth remained free of microbial growth for indefinite
period.
• He also developed a sterilization method “Tyndallization”,
referred as intermittent or fractional sterilization.
Hans Christian Gram (1853 – 1933):
• Developed a staining procedure for differentiating two
different group of bacteria, based on the cell wall structure
(Gram +ve and Gram –ve).
• The staining is called Gram staining.

16. Robert Koch (1843 – 1810):
• Isolated bacilli from bloods of cattle and infected with
healthy one and observed the disease.
• He proved that microorganisms cause the disease.
• He formulated a sequence procedure to prove that specific
microbes cause the specific disease, called as Koch’s
Postulate.

17. Koch's postulates
Robert Koch (1843-1910) was the first to prove in 1876 that the
animal disease, anthrax is incited by a bacterium, Bacillus
anthracis
He put forth the famous ‘Koch’s postulates’ for proving that a
particular organism is the cause for a particular disease.
1. The suspected causal organism must be found associated with the
disease in the plants.
2. It must be isolated and grown in pure culture on nutrient media.
3. When a healthy plant is inoculated with it, the original disease
should be reproduced.
4. The same organism must be re-isolated in pure culture from
experimentally infected plant and its characteristics must be
exactly like that of original culture.

19. Naturally diseased
Isolation
Culturing
Spore
Healthy leaf
Inoculation
Artificially diseased
Re-isolation
Confirmation

20. Joseph Lister (1878):
• Developed Pure culture technique.
• Pure culture referred as the growth of moss of cells of same species
in a vessel.
• He developed the pure cultures of bacteria using serial dilution
technique.
• He also discovered that carbolic acid to disinfect the surgical
equipment and dressings.
Alexander Fleming (1928):
• Identified Penicillium notatum inhibiting Staphylococcus aureus
and identified the antibiotic Penicillin
Selman. A. Waksman (1945):
• Identified Streptomycin antibiotic from soil bacterium.
• He also coined the term antibitiotics (referring a chemical
substance of microbial origin, which is in small quantity exert
antimicrobial activity).

21. Martinus Willium Beijerinck (1851-1931):
• Developed enrichment technique to isolate bacteria.
• Isolated sulphur reducing bacteria and sulphur oxidizing
bacteria from soil.
• Isolated free living nitrogen fixing bacterium (Azotobacter)
from soil. Identified root nodulating bacterium Rhizobium,
Lactobacillus, gree algae.
• He confirmed Tobacco mosaic virus and coined the term Virus.
Sergei Winogradsky (1856-1953):
• Identified microorganism involved in N cycle, C cycle, S cycle.
Nitrification process in soil.
• Chemolithotrophic nutrition in soil bacteria.
• Discovered anaerobic nitrogen fixing bacterium Clostridium
pasteurianum

23. Thank You